Seal for thin tubing



| R. RUBIN 3,437,357

SEAL FOR THIN TUBING April 8, 1969 Filed Feb. 1, 1967 INVENTOR. 25 H LEONARD R. RUBIN FIG. 3 /flwxw ATTORNEY United States Patent 3,437,357 SEAL FOR THIN TUBING Leonard R. Rubin, Union, N.J., assignor to Engelhard Industries, Inc., Newark, N.J., a corporation of Delaware Filed Feb. 1, 1967, Ser. No. 613,149 Int. Cl. F16] 19/00 US. Cl. 285-55 5 Claims ABSTRACT OF THE DISCLOSURE This disclosure pertains to seals useful in securing thin tubes to a tube sheet, and wall or the like. The seals are useful in hydrogen diffusion apparatus which utilize tubing made from palladium or palladium alloys. A special type of seal using ferrules of different hardness and a tube brace is found to greatly decrease the tendency of the seal to leak.

Background of the invention This invention relates to a seal for securing a thin tube to an end wall, a header, a tube sheet and the like. When purifying hydrogen by use of palladium or palladium alloy diffusion tubes, it has been found that leaks develop in seals at the point of connection of the thin tubes to another portion of the apparatus, such as an end wall, header or tube sheet. These problems normally arise because of the unusual characteristics of palladium and palladium alloys in expanding in the presence of hydrogen. The hydrogen is absorbed and desorbed causing expansion and contraction of the tubing thereby rendering quite difficult the obtaining of effective and durable seals.

Seals used heretofore have been found sorely lacking in ability to endure the conditions present in hydrogen diffusion units. General purpose mechanical seals, e.g. tube couplings described in US. 2,484,815 are not suitable for the stringent conditions peculiar to hydrogen purification by use of thin palladium and palladium alloy tubing. The seals in the art generally fail to relate to the desirability of using ferrules of varying hardness. These known seals do not perform satisfactorily in hydrogen diffusion apparatus.

Purification apparatus utilizing tubes of gas permeable metal are ordinarily one of two general types-the in-out type and the out-in type. In both, the diffusion tube (or tubes) extends into a chamber with the bore of the tube sealed from the chamber. In the in-out type impure feed gas containing hydrogen is fed into the bore of the tube under pressure and the hydrogen diffuses out through the walls of the tube itno the chamber. In the out-in type the diffusion is in the opposite direction. The feed gas is fed into the chamber under pressure and the hydrogen difiuses into the bore of the tube. In conventional in-out apparatus each tube is normally secured and sealed through the walls of the chamber at two points-ordinarily at opposite ends of the chamber-since both ends of each tube open outside the chamber for feed gas containing hydrogen to be fed in one end and undiffused gas to flow out the other. The tube may, however, also be sealed at one end of the chamber. It is these seals with which an aspect of the present invention is concerned.

Summary This invention concerns a novel seal for securing thin tubing which seal comprises threaded portions, a brace, and ferrules of differing hardness. It is also concerned with gas diffusion apparatus utilizing the seal.

According to the present invention, it has now been found that a tight reliable seal can be made in hydrogen diffusion units comprising thin tubes of palladium or palladium alloy by utilizing an easily assembled and disassembled fitting and brace having particular compressability and structural relationships. These relationships include the use of ferrules of varying hardness which permit a minimum of deformation of the diffusion tubes involved and n0 leakage at the connection. These advantages allow continued and uninterrupted purification of the hydrogen.

It is an object of this invention to provide a novel means for readily and inexpensively attaching thin palladium or palladium-alloy diffusion tubes to an end wall, header, tube sheet, and the like. A still further object is provision of hydrogen diffusion devices utilizing the novel seal described in detail hereinbelow. Other objects will be apparent from the following description of this invention.

Brief description of the drawings Referring to the accompanying drawings, preferred embodiments of the devices of the present invention are shown in which:

FIGURE 1 is a sectional side view of the seal of this invention in disengaged position, and the tubing used in conjunction therewith;

FIGURE 2 is a sectional side view of the seal of this invention in tightened or engaged position, and the tubing used in conjunction therewith; and

FIGURE 3 is a sectional side view of one type of device for purifying hydrogen in which the seal of this invention is utilized.

Description of the preferred embodiments Referring to FIGURE 1 of the drawings, the novel seal of this invention consists of the body portion 1 having a bore coextensive therewith 2 and some means 3 such as a weld for connection to an end wall, header, tube sheet, or the like 4. Said body portion also has an external screw thread 5 and a frusto-conical inner surface 6 at one end of the bore 2. The tube 7 to be tightly secured is disposed within the bore 2.

A hard cylindrical brace 8 is disposed inside the tubing 7 and is preferably held in place by the frictional force which exists due to the bearing of the brace 8 against the tubing 7. This tubing is normally composed of palladium or a palladium alloy particularly useful in permitting hydrogen diffusion therethrough. Palladium alloys known to be useful in this regard are palladium-silver, palladiumboron, and palladium-gold. A particular suitable alloy for hydrogen diffusion contains, by weight, Pd-% and Ag-25%.

The ferrule 9 is free in the open position to slide along the tubing 7. It is referred to as a soft ferrule. This term is intended to point out its relative hardness or ability to deform as compared with the deformability of metal used for the brace 8. Metals normally making up such soft ferrule may include copper, annealed monel, silver, aluminum, and the like. It is preferred, although not essential, that the surface of the soft ferrule may be roughened to prevent rotation of the tubing at the time of tightening of the seal. This may be accomplished by formation of a film on the ferrule, such as an oxide film. It has been found that annealing in air at a temperature of about 650 C. causes formation of an oxide film on monel, a preferred ferrule material. This oxidized surface has been found useful in preventing rotation of diffusion tube during tightening of the seal.

This soft ferrule has an inside surface 10, a tapered external surface 11, and a surface 12 opposite said tapered external surface 11. Said tapered external surface 11 has an included conical angle approximating the included conical angle of the frusto-conical inner surface 6.

The ferrule 13 is also slidably disposed on the tubing and is referred to as a hard ferrule. It is intended that this term refer to ferrules made of materials more difficultly deformable than the metal of which the soft ferrule is composed. This hard ferrule may normally be made from stainless steel, cold worked monel, carbon steel, and the like. The brace 8 is also termed hard and is preferably stainless steel, carbon steel, or the like. The hard ferrule 13 is contiguous to the soft ferrule 9 and is disposed so that its movement along the tube in the direction of the body 1 will cause bearing between its tapered end 14 and the soft ferrule '9 on surface 12 opposite the tapered external surface 11.

A tightening member 15 slidably and rotatably disposed on the thin tubing has internal screw threads 16 for use in engagement with the external screw threads of the body 1 and an internal bearing surface 17. It is capable of bearing contact with the fiat end 18 of the hard ferrule 13. This tightening member 15 is of such size to encase the two ferrules 9 and 13. Lubricant such as mineral oil may be applied to surfaces 17 and 18 to prevent rotation of the tubing 7 during the tightening of the seal. When brought into threading engagement with the body 1, the tightening member 15 causes bearing against the flat end 18 of the hard ferrule which in turn causes sliding engagement between the tapered end 14 of the hard ferrule 13 and the surface 12 opposite the tapered external surface 11 of the soft ferrule 9. This progressively causes bearing between the tapered external surface 11 and the frusto-conical inner surface 6 of the body 1, and the inside surface of the soft ferrule 9 and the thin tube 7. The hard cylindrical brace 8 is so positioned within the thin tube 7 as to prevent bending thereof when the inner surface 10 of the soft ferrule 9 is biased against the tubing 7 after tightening of the tightening member 15.

The tightening member may have a knurled hexagonal or similar gripping surface 19 so as to permit easy tightening. When in threaded engagement with the body 1, the tightening member 15 will embrace, in addition to the fer-rules 9 and 13, a portion of the body 1 and at least a portion of the hard cylindrical brace 8. The relationship of the various parts of the seal of this invention and the thin tubing in the above described tightened or closed position is shown in FIGURE 2.

Referring to FIGURE 3, the gas purification apparatus shown is one of many possible designs utilizing the novel seals of this invention. It comprises generally one or a plurality of diffusion tubes 7 (preferably coiled) supported between a pair of end walls 20 and 21 of a collecting chamber 22. This chamber 22 is formed by a shell 23 and the end walls 20 and 21. An outlet tube 24 provide means for exit of diffused gas. An inlet 25 provides means for supplying crude gas to inlet chamber 26 and outlet 27 permits removal of off-gas from outlet chamber 28. The novel seal of this invention 29 provides inventive means for attaching diffusion tubes 7 to the end walls 20 and 21. In a modification of the equipment shown in FIGURE 3, a single end Wall supporting one or more diffusion tubes closed at an end thereof inside the chamber 22 may be used.

The seal of this invention has been used to secure thin palladium-silver alloy hydrogen diffusion tubes to a header in hydrogen diffusion equipment and has successfully prevented gas leakage after hundreds of hours of use.

Heating and cooling the diffusion unit times between and 450 C. has also failed to cause leakage.

What is claimed is:

1. In a seal for tightly securing thin H permeable tubing consisting essentially of palladium or a palladium alloy having a body portion with a bore therethrough, connecting means at one end of the body, a frusto-conical inner surface at the other end of the body, and an axially-bored internally threaded tightening member slidably and rotatably disposed on said thin tubing and having an internal bearing surface, the improvement comprising (a) an axially-bored hard metal ferrule slidably disposed on said thin tubing,

(1) a tapered end at one end of the bore, (2.) a fiat end at the other end of the bore;

(b) a hard cylindrical brace co-axial with, inside of,

and bearing against said thin tubing;

(c) an axially-bored soft metal ferrule constructed and arranged for scalability, stability and inhibiting hydrogen diffusion at temperatures above 150 C. and being slidably disposed on said thin tubing, positioned between and adjacent the frusto-conical inner surface of the body and the tapered end of the hard ferrule and adapted to slidably engage the tapered end of the hard ferrule,

said tightening member seated adjacent the fiat end of the hard ferrule, adapted to be brought into threading engagement with the external screw thread of the body, and, when brought into threading engagement with the body, encasing the hard ferrule, the soft ferrule, the thin tube, and the hard cylindrical brace, causing bearing between (1) the tapered end of the hard ferrule and the surface opposite the tapered external surface of the soft ferrule, (2) the frusto-conical inner surface of the body and the tapered external surface of the soft ferrule, and (3) the inside surface of the soft ferrule and said thin tubing.

2. A seal according to claim 1 wherein the surface of the soft ferrule is roughened to prevent rotation of the tubing during tightening of the seal.

3. A seal according to claim 2 wherein the surface of the soft ferrule is roughened by oxide formation.

4. A seal according to claim 2 wherein the fiat end of the hard ferrule and the internal bearing surface of the tightening member are lubricated to prevent rotation of the tubing during tightening.

5. A seal according to claim 4 wherein the soft ferrule is composed essentially of annealed monel and the hard ferrule is composed essentially of stainless steel.

References Cited UNITED STATES PATENTS 2,761,704 9/1956 Crawford 285249 2,961,062 11/1960 Hunter et a1. 55-158 3,103,373 9/1963 Lennon et a1. 285-3827 3,215,457 11/1965 Teeters 285382.7 3,251,173 5/1966 Ehlers et. al. 55158 3,274,754 9/1966 Rubin 55-158 3,375,025 3/1968 Engel 285248 REUBEN FRIEDMAN, Primary Examiner.

CHARLES N. HART, Assistant Examiner.

US. Cl. X.R. 

